The present invention relates to a magnetic memory device comprising a thin-film magnetic head constructed in layers on a nonmagnetic substrate for use with a recording medium which is provided with a magnetizable storage layer of a material with predetermined coercivity, in which information can be written along a track by perpendicular (vertical) magnetization of the layer, where the magnetic head contains a magnetic conduction body which is similar to a ring head and carries the magnetic flux with two magnet legs, each of which comprises at least one magnetic layer with predetermined magnetic behavior. Further, the magnetic poles facing the recording medium are arranged in tandem as seen in the (relative) direction of motion of the head, a gap of predetermined width being formed between the poles, and outside the pole region an intermediate space is defined between the legs, through which the turns of the writing and/or reading coil winding extend.
A corresponding magnetic head of such a memory can be seen, for instance, from European Patent Application No. 0 012 912 A1. With this head, information can be stored by vertical magnetization of an appropriate recording medium. This principle is generally known (see, for instance, "IEEE Transactions on Magnetics", Vol. MAG-16, No. 1, Jan. 1980, pages 71 to 76, or Vol. MAG-20, No. 5, Sept. 1984, pages 657 to 662 and 675 to 680). The recording media which are to be provided and are frequently also designated in principle as vertical magnetization can be provided in the form of rigid magnetic memory discs, individual flexible discs (floppy discs) or magnetic tape. These media comprise at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material of predetermined coercivity, especially of a CoCr alloy. The axis of the so-called easy magnetization of this layer is oriented perpendicularly to the surface of the medium. By means of special magnetic heads, information can then be written in along a track as bits in successive sections by appropriate magnetization of the storage layer.
The combined read and write magnetic heads known for the principle of so-called longitudinal magnetization, however, cannot be applied directly to vertical magnetization. Although, if these heads are used, wherein the magnetic conduction body formed by the magnet legs generally has a shape similar to a ring head, the magnetic flux desired for utilizing the principle of vertical magnetization, to form a circuit closed as far as possible with low magnetic resistance, can be obtained, it is difficult to generate a sufficiently strong writing field at high bit densities and due to this, with a correspondingly small length of the so-called air gap which is formed between the magnetic poles of the ring head facing the recording medium.
One is therefore compelled to develop special magnetic write-read heads for the principle of vertical magnetization. The design of such a head can be seen, for instance, from the European Patent Application cited above. This known magnetic head comprises a so-called conduction body for conducting the magnetic flux. This magnetic conduction body is formed by two magnet legs which consist of at least one layer of a magnetic material with predetermined specific magnetic properties or magnetic behavior such as of a special NiFe alloy (for instance, "Permalloy"; Trade Mark of "Bell Telephone Manufacturing Company"). With the end regions facing the recording medium, two magnetic poles are formed which are arranged in tandem as seen in the direction of relative motion of the head and medium and with a predetermined small gap width relative to each other. These end regions are followed by a region of the head in which the magnet legs are brought to a larger mutual spacing. In this manner, a sufficiently wide space between the magnetic legs is obtained, through which the turns of a write and read coil winding extend. For the writing function as well as for the reading function of this magnetic head, the ring-head-like form of its magnetic conduction body with both magnetic legs is utilized.
The individual parts of this known magnetic head are applied by a thin-film technique to the flat back side of a nonmagnetic substrate. This technique is generally known for magnetic write/read heads (see, for instance, "Feinwerktechnik und Messtechnik", Vol. 88, No. 2, Mar. 1980, pages 53 to 59, or "Siemens-Zeitschrift", Vol. 52, No. 7, 1978, pages 434 to 437). However, the generation of sufficiently strong write fields while maintaining at the same time high resolution for reading is a problem in such magnetic thin-film heads. These two requirements are basically contradictory, since generally strong magnetic fields can be obtained only with large gap width and/or large pole thicknesses, while high resolution for high bit density can be achieved only with small gap width and/or small pole thicknesses (see, for instance, "IEEE Transactions on Magnetics", Vol. MAG-19, No. 5, Sept. 1983, pages 1617 to 1619). In addition, the writing field should be as asymmetrical as possible in a magnetic head for vertical recording in order to raise the vertical component of this field at the trailing edge of the writing magnetic pole and to attenuate the vertical component of opposite polarity at the leading edge of the other magnet pole. In the known magnetic head type, the magnetic field at the trailing edge is generally somewhat weaker than the magnetic field at the leading edge.